HONOLULU (AP) — Hawaii on Monday said a vaccinated Oahu resident who traveled to Nevada last month has tested positive for the delta variant of COVID-19, a highly transmissible strain of the disease.

The delta variant was first detected in India. Scientists in the United Kingdom, where it is now the most common form of the disease, estimate it is between 40% and 80% more transmissible than the previous dominant strain.

The variant currently makes up 6% of all cases in the U.S, the Hawaii Department of Health said.

Health Director Dr. Libby Char described this as a “very rare breakthrough” case in which a COVID-19 vaccine didn't prevent infection. She said the COVID-19 vaccines not only help protect against infection but also severe illness.

New analysis Monday from Public Health England showed that two doses of the main vaccines in the U.K.’s rollout are highly effective against hospitalization from the delta variant, including the Pfizer vaccine widely used in Hawaii and the United States.

The analysis showed the Pfizer vaccine is 96% effective against hospitalization after two doses while the AstraZeneca jab is 92% effective.

Hawaii's health department said the individual who caught the delta variant was fully vaccinated for COVID-19 before traveling and had tested negative for COVID-19 before leaving Nevada for Hawaii.

The individual developed mild symptoms several days after returning home and tested positive. The department said the person went into isolation and their household and close contacts were quarantined.

The state hasn’t found evidence that anyone caught COVID-19 from this person.